2- Ethoxy-3,4,5,6-tetrahydropyridine

Tetrahydro-ll//-pyrido[2,l-b]quinazolin-ll-one (7) was formed only in 3% and 7% yields when 2-iodoaniline was reacted with 2-piperi-done and 2-ethoxy-3,4,5,6-tetrahydropyridine, respectively, in the presence of potassium carbonate, catalytic amount of palladium(II) acetate, and triphenylphosphine in hexamethylphosphoric triamide at 110°C for 24 h under an atmosphere of carbon monoxide [85H(23)2803]. 

Depending upon the reaction conditions, 2-ethoxy-3,4,5,6-tetrahydropy-ridine and isopropylidene 2-acetylmalonate afforded either perhydropy-rido[2,l-h][l,3]oxazine-2,4-dione (162) or hexahydropyrido[2,l-b][l,3]ox-azine-3-carboxylic acid (163) (86MI1). Reaction of 2-methoxy-3,4,5, 6-tetrahydropyridine with diketene without a solvent gave a mixture of 4H-quinazolin-4-one (164) and hexahydropyrido[2,l-h][l,3]oxazin-4-one (165) [75H(3)927]. 

No comparison between trialkyloxonium fluoroborates and dialkyl sulfates has been made, but analysis of available data shows that oxonium salts are more generally applicable reagents for the preparation of lactim ethers. The alkylation of 3-carbethoxypiperid-2-one (7)25 and morpholin-3-one (8)32 with dimethyl sulfate failed, but with triethyloxonium fluoroborate these compounds gave 2-ethoxy-3-carbethoxy-3,4,5,6-tetrahydropyridine (9) and 3-ethoxy-3,4-dehydro-morpholine (10) in excellent yield. The selective character of triethyloxonium fluoroborate is shown in its reaction with 3,3-diethyl-5-methylpiperidine-2,4-dione (11 ).25 Reaction of 11 with the calculated quantity of dimethyl sulfate resulted in alkylation of the carbonyl group in position 4 with formation of 12, but reaction of 11 with triethyloxonium fluoroborate gave the lactim ether (13). 

In the presence of sodium ethoxide in ethanol, the urethane synthesis starting from 4-amino-l-benzyl-i,2,5,6-tetrahydropyridine-3-carbonitrile and diethyl carbonate affords as a byproduct 6-benzyl-4-ethoxy-5,6,7,8-tetrahydropyrido[4,3-d]pyrimidin-2(lA/)-one (6).496... 

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